Recently, there have been demands for a magnetic disk device to have large capacity, high recording density and high access. To meet these demands, a disk and a head gimbal assembly are rotated and driven at a high speed respectively, which creates a certain amount of air turbulence, thereby producing vibration in the disk and head gimbal assembly. The turbulence vibration hinders a head from being positioned on a high-density recorded disk data. The reason is that air turbulence is randomly created, which makes it difficult to estimate its size and period, making it complicated and difficult to control a quick and accurate positioning. In addition, the turbulence vibration produces noise, which leads to a loss of the quietness of the device.
Aside from the above, the air turbulence created by a high speed rotation in the device causes a problem with increase in consumption power. The rotation of a disk at a high speed involves and rotates air around the disk. On the other hand, air away from the disk is stationary, generating a shearing force therebetween which turns into a load to stop the rotation of the disk. This is referred to as “windage loss,” and the faster the disk rotates, the greater the loss. Rotating the disk at a high speed against the windage loss requires a motor to deliver a large output, which needs a large electric power in turn.
While attention is focused on the turbulence and windage loss being proportional to the density of gas in the device, there has been an idea that low-density gas instead of air is sealed in a hermetically sealed magnetic disk device to decrease the turbulence and windage loss. Hydrogen and helium are candidates as low-density gases. Taking into account its practical use, helium is optimal as it is more effective, stabler, and safer. A magnetic disk device in which helium gas is hermetically sealed, can solve the above problem and realize a quick and accurate positioning, saving power and sufficient quietness. However, there has been a problem in that helium readily leaks out during use from a housing used in an ordinary magnetic disk device inferior in hermetic because helium is very small in molecule and large in diffusion coefficient.
U.S. Patent Publication No. 2005/0068666 (“Patent Document 1”), for example, discloses a technique which enables low-density gas such as leaky helium, to be hermetically sealed. FIG. 10 is a cross section of the hermetically sealed magnetic disk device described in Patent Document 1. A head disk assembly 31 is fixed to a base 32 and sealed into a housing with a cover 33. A part where helium in the housing is most apt to leak out is a junction 34 of the base 32 with the cover 33. The cover 33 is laser-welded or soldered to the upper part of the side wall of the base 32 at the junction 34.
Another place where helium in the housing is most apt to leak out is the opening of the base 32 to which a feedthrough 40 connecting an FPC assembly in the housing to a circuit board outside the housing is fitted. FIGS. 11 and 12 are a side view and top view of the feedthrough 40 respectively. The feedthrough 40 has a flange 41 and a plurality of pins 43 fixed to the flange 41 by a glass sealing material 44 and is fixed by bonding the flange 41 to the periphery of the opening in the bottom of the base 32 by solder.
However, solder used for bonding the feedthrough to the base is low in proof stress as material, so that it may not ensure sufficient bonding reliability depending on external force applied to a magnetic disk device or unexpected deformation caused by change in temperature environment while the magnetic disk device is used.